The present invention relates generally to a method and apparatus for continuous production of partially polymerized compositions and polymers therefrom.
Polymers form the basis for many important materials. For example, adhesives are one important type of material typically based on polymers. Adhesives can be provided in various forms for application, often depending on how polymers on which they are based are themselves formed. For example, polymer-based adhesives can be prepared and provided in organic solvent for application, after which time the solvent is removed. Polymer-based adhesives can also be prepared and applied without use of organic solvent—for example, as in the case of hot-melt adhesives (i.e., where the adhesive is substantially polymerized prior to its application to a substrate) or web-polymerized adhesives (i.e., where the adhesive is substantially polymerized after its application to a substrate).
Methods for preparation of polymers and materials (e.g., adhesives) based thereupon can be performed in a continuous or batch-wise manner. In contrast to continuous web-polymerized methods, conventional methods of batch polymerization of adhesives and methods of continuous production of hot-melt adhesives typically involve running of an initial polymerization reaction to at least near complete conversion, and often complete conversion, of the monomer to polymer. In both cases, the adhesive is substantially polymerized prior to its application to a substrate as compared to web-polymerized adhesives (i.e., where the adhesive is substantially polymerized after its application to a substrate, as discussed above).
Nevertheless, in order for a polymerizable composition to be capable of forming and maintaining an adequate coating (i.e., a cohesive coating) for web-polymerization, it is known to be desirable to partially polymerize the composition before forming the coating on-web. See, for example, U.S. Pat. No. 6,866,899, for a discussion of partially polymerized syrup formation when coating a composition onto a substrate for polymerization. Although the web-polymerization itself may be a continuous process, formation of such a syrup is typically a batch process, with the syrup being prepared in a batch polymerization reactor. See, for example, U.S. Pat. Nos. 4,181,752 and 4,303,485. In addition to process inefficiencies inherent in batch processes as opposed to continuous processes, however, conventional batch processing has other disadvantages.
For example, U.S. Pat. No. 7,119,128 discusses the problem of achieving adequate distribution of free radicals generated by ultraviolet radiation throughout a batch polymerization reactor due to limited depth of penetration of ultraviolet radiation therein. In order to assist in overcoming this problem, stirrers and/or other equipment modifications are generally required to be used in such batch polymerization reactors.
U.S. Pat. No. 7,015,295 discusses the difficulty in adequately controlling batch polymerization reactions due to the large exotherm produced upon generation of free radicals when using thermal radiation. In order to assist in overcoming this problem, certain polymerization initiators and processing temperatures must be used according to the methods therein.
Thus, alternative processing methods for web-polymerization and formation of syrups for polymerization on-web are desirable. In addition to the need for alternative processing methods, a need for alternative processing equipment also exists.
While most conventional polymer processing equipment for continuous processes is configured to be substantially horizontal, it is known to utilize a vertical or elevated equipment configuration. German Patent No. 880938 discloses a method of continuous emulsion or suspension polymerization where a vertical tube with partial or continuous agitation is utilized for the select polymerization reactions therein.
U.S. Pat. No. 4,089,918 describes a process for the continuous casting of liquid polymerizable compositions. The compositions are polymerized via thermal polymerization. According to the process described therein, monomer is first partially polymerized and then further polymerized to a degree of polymerization of about 40-60% between a pair of moving belts. The path of the moving belts from a point where the polymerizable composition is inserted therebetween may be straight in a horizontal direction, inclined at a suitable angle to the horizontal, or curved to follow a natural curvature that may be defined by the moving belts when arranged so as to be inclined at a suitable angle to the horizontal.
Nevertheless, in view of environmental and safety concerns as well as the ever-present desire to optimize production efficiency, alternative methods and apparatus for production of further partially polymerized compositions, such as those on which many adhesives are based, are desirable. Particularly desired are alternative methods and apparatus for the continuous production of partially polymerized compositions as well as polymers therefrom.